Processes and systems for the production and distribution of audio material, and the audio component of audiovisual material, frequently need to change the audio source that is to be supplied to a particular audio destination. Such changes to the ‘routing’ of audio signals may take place in ‘audio mixers’ or ‘switching matrices’. These devices may handle only audio signals, separate audio and video signals, or combined audio and video signals.
Mixers usually provide means for crossfading between different audio signals, whereas switching matrices (also known as audio routers) usually change almost instantaneously between different audio sources. A typical audio switching matrix may include some audio processing functions, for example adjustment of audio gain or delay, or the separation or combination of audio and video signals. However, control of the transitions between different audio sources is not usually provided. In this case, a virtually instantaneous change in the value of an output audio signal at a destination will occur when switching between different audio sources.
Such changes can be subjectively disturbing to a listener as, depending on the content of the switched audio, they may represent unnatural ‘pops’ or ‘clicks’. In some cases, it is necessary to process the audio signal in real-time, thus limiting the available options for processing and/or potentially requiring very large processing resources. In addition, audio switching matrices often have very large numbers of input sources and output destinations, which again may imply a need for very large processing resources. It would however clearly be preferred if the switching process could be implemented with only minimal processing resources. There is thus a need for a simple and easily-implemented method and apparatus for improving the subjective effect of changes to the routing of audio signals.